Thermoplastic vinyl based technology directed to replacement of metal and higher performance engineering thermoplastics in AO end-uses for instance, is gaining momentum. This is a departure from traditional uses pertaining to extrusion related PVC art. PVC, viewed from a commodity resin perspective, is known for limited dynamic thermal stability and high melt viscosity. As a result of advancements in resin quality and compound formulation, improved single phase PVC formulations directed to overcoming these and other limitations are making inroads in custom injection molding compound (CIM) for a variety of end-use markets including the aforesaid appliance and office automation (AO) business machine housing markets.
Specifically, the pertinent art is directed generally to providing higher melt flow and reduced melt viscosity of PVC compounds while maintining or desiredly improving heat deflection temperature (HDT). These are commercially valuable property combinations characteristic of higher valued, more crystalline engineering thermoplastics. U.S. Pat. Nos. 4,339,554, 4,458,046, and 4,469,845 describe PVC polyblends containing copolymers of styrene and maleimide. These disclosures are directed to various copolymers of styrene and imide derivatives of maleic anhydride blended with PVC resins in order to obtain increased HDT. Impact modifiers are suggested in U.S. Pat. Nos. 4,469,844 and 4,469,845 which describe improved polyblends of grafted rubber-modified vinyl chloride resins. The polyblends optionally contain ABS, MBS, or an ungrafted rubber and exhibit higher softening temperatures than that of the vinyl chloride resin.
U.S. Pat. No. 4,595,727 teaches a methacrylate derived imide blend with rubber modified PVC comprising: 10% to 90% by weight of a polyglutarimide with 90% to 10% by weight of rubber modified PVC. The polyglutarimide is prepared by reacting an acrylic polymer, particularly polymethyl methacrylate or a copolymer of methyl methacrylate and a minor amount of an ethylenically unsaturated comonomer, with an aminating agent such as ammonia or alkyl amine. The rubber-modified vinyl chloride resin is prepared by polymerization of vinyl chloride in the presence of 2 to 50 percent, based on the weight of the resin, of a rubber to form a graft copolymer.
Kokai application number 56-159243 describes a blend of glutarimide polymer exhibiting a higher heat deflection temperature, however it is also demonstrated that melt flow is reduced. For AO injection molding PVC based compounds, higher melt flow rates would be desired. Kokai application Number 2-142845 provides an improved melt flow component for a PVC/glutarimide blend comprising a polyolefin or polystyrene diblock with methacrylate, PVC, .epsilon.-caprolactone, EVA, SMA, and others. Preferred amounts of this diblock range from 0.5-10 weight parts. The glutarimide is present at 5-50 parts.
An approach aiming at direct modification of particulate PVC resin can be found in U.S. Pat. No. 4,814,387 pertaining to PVC treated with a low I.V., high glass transition temperature improving agent. The method of treatment is overpolymerization on PVC resin of a high glass transition temperature composition in combination with molecular weight modifying amounts of chain transfer agent. The overpolymerization component consists of polymerized monomers selected from styrene and its derivatives, vinyl nitriles, methacrylates, maleimides, with the preferred component consisting of a copolymer of .alpha.-methyl styrene and acrylonitrile.
A single phase morphology CPVC composition is disclosed in U.S. Pat. No. 4,847,331 wherein a blend of CPVC having a chlorine content of between about 60% and 66% by weight is combined with a polymethylmethacrylate comprising not more than 80% by weight of the blend. Within the specified chlorine content, the composition of matter displays homogeneous, substantially single phase behavior with the CPVC and polymethylmethacrylate being substantially or completely miscible. The resulting blended material exhibits enhanced temperature and durability properties and remains homogeneous up to a temperature of 230.degree. C. CPVC generally exhibits significantly higher melt viscosity than a comparable molecular weight PVC. This is substantially a result of appreciably lower melt flow at useful chlorine levels of 63-67% yet these resins are established for higher continuous use temperatures.
A ternary blend of PVC/Polycarbonate/ABS is disclosed in U.S. Pat. No. 3,882,192. Particularly preferred blends contain from 30-50 parts of each component. The preferred method of preparation involves a first combination of PVC and ABS, followed by combination of this blend with polycarbonate. Impact strength and heat distortion temperature are notably enhanced.
A single phase PVC modified with a high melt flow shear modified polypropylene is disclosed in U.S. Pat. No. 4,665,118. This disclosure does not reveal that a significant limitation in attaining acceptable impact strength is observed with blends of the disclosed polyolefin and PVC. It is well established that this is an incompatible combination. The polypropylene acts generally as a fusion retardant in an external lubrication function. With regard to HDT, such a blend would result in no appreciable loss in HDT, however not an insignificant amount of an impact modifier would nonetheless be required. The presence of this modifier expectedly would decrease both melt flow and HDT which is an undesired effect.
U.S. Pat. No. 4,267,084 discloses a blend of a major amount of a first higher molecular weight (I.V.) PVC with a minor amount of a lower molecular weight PVC. The blend is disclosed as exhibiting improved thermal stability compared to a blend wherein the lower I.V. PVC is not modified with a mercaptan or disulfide compound. The compositions disclosed contain from 70 weight parts to about 90 weight parts of a PVC having degree of polymerization (DP) of 1020 and 1320, with 30 to 10 weight parts of a lower molecular weight PVC having DP of between 130 to about 580. In this blend it is the higher I.V. PVC which is present in the major amount and dominates the properties of the continuous phase.
Owing to the present variety of methods aimed at enhancing PVC compounds particularly for injection molding uses, the attendant antagonistic relationships between melt flow, impact modification and HDT remain as limitations for enhancements. It would be desirable to arrive at a PVC blend exhibiting adequate melt flow and inherently better impact properties thereby requiring less conventional impact modification. Attaining the desired level of impact strength with reduced levels of conventional impact modifiers would be advantageous due to the deleterious effects of these modifiers on melt flow rate, melt viscosity, HDT, weatherability and dynamic thermal stability.